The Temple of Karabor was the center of draenei worship until its priests were slaughtered by demonically corrupted orcs. In the massacre's aftermath the warlocks of the Shadow Council seized the structure and gave it a new name: the Black Temple.
When the Alliance invaded Draenor after the Second War, the orc shaman Ner'zhul hastily opened several dimensional portals in order to escape. The resulting magical backlash ripped the world apart. Drawn by these portals, the pit lord Magtheridon arrived in what had come to be known as Outland and took the temple as his seat of power.
His dominion over Outland remained unchallenged until the arrival of Illidan the Betrayer. The pit lord proved no match for the wielder of the Twin Blades of Azzinoth. Today Illidan occupies the temple, awaiting any and all who would challenge his rule.